CHICAGO — After spending 54 hours removed from the driver’s seat, the Mets plunked themselves back into it Tuesday night.

Methodically, they overcame a brutal David Peterson start and ugly defensive play, finally going ahead after the Reds had already lost their game against the Pirates.

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And then, after the Cubs had tied it, Francisco Alvarez delivered his biggest career hit: a two-run homer in the eighth that put the Mets ahead for good in a 9-7 victory at Wrigley Field.

And so, the National League’s third wild-card is again the Mets’ to lose.

The Mets moved one game ahead of the Reds (who lost 4-2).

The Reds own the tiebreaker against the Mets based on winning the season series.

Alvarez cleared the ivy in left-center with two outs in the eighth, two days after he was robbed of a potential game-tying homer in the ninth inning by the Nationals’ Jacob Young.

The Mets received another big homer on this night from Brandon Nimmo, whose three-run blast in the fifth completed the team’s comeback from a 6-1 deficit.

Taking no chances, manager Carlos Mendoza deployed Edwin Díaz for a six-out save. Díaz finished the job.

Peterson, in just his latest awful performance, allowed five earned runs on five hits and two walks over 1 ¹/₃ innings. The lefty’s free fall over the past two months includes four starts in his past eight in which he’s allowed at least six earned runs.

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Francisco Lindor swatted the game’s second pitch into the bleachers in left-center for his 10th leadoff homer this season. It was Lindor’s 29th homer this season, moving him to the brink of joining Juan Soto and Pete Alonso among Mets players with at least 30.

But the Cubs jumped on Peterson and took advantage of a defensive lapse in the bottom of the inning. Carlos Santana stroked a two-run double — a ball that Juan Soto misjudged in right field that should have been the final out — putting the Mets in a 2-1 hole after Nico Hoerner singled leading off and Carson Kelly walked.

Peterson got knocked out in the third on Ian Happ’s two-run double that extended the Cubs lead to 5-1. Hoerner delivered an RBI single for the inning’s first run after Justin Turner walked leading off, Matt Shaw singled and Pete Crow-Armstrong sacrifice bunted the runners to second and third.

Jeff McNeil committed consecutive throwing errors in the fourth to help widen the Mets deficit to 6-1. McNeil threw away the relay from Mark Vientos on Hoerner’s grounder as he attempted to complete a double play. The next batter, Happ, hit a grounder that McNeil fielded in the hole and fired past Pete Alonso for an error, allowing Hoerner to score.

Nimmo resurrected the Mets with a three-run homer in the fifth that tied it 6-6 after his team had already scored twice in the inning. Nimmo greeted lefty reliever Taylor Rogers with a shot that cleared the right field wall for his 25th homer this season.

Dansby Swanson’s fielding error on Alvarez’s grounder opened the gate for the Mets to score five unearned runs in the inning. Alonso brought in two of them with a single off the right field ivy after Michael Soroka had walked Soto with two outs.

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Lindor’s RBI single in the sixth gave the Mets a 7-6 lead after McNeil stroked a two-out double and Alvarez walked.

Gregory Soto allowed a two-out single to Hoerner in the sixth before Tyler Rogers entered and walked Happ. Seiya Suzuki’s ensuing RBI single tied it 7-7.

Justin Turner singled against Tyler Rogers with two outs in the seventh and Matt Shaw walked. But Brooks Raley stifled the threat by striking Crow-Armstrong to keep the game tied.

In the eighth, Brett Baty blooped a leadoff single and pinch-runner Luisangel Acuña stole second before Alvarez homered against Caleb Thielbar to give the Mets a 9-7 lead.